4b - Computer systems - hardware Flashcards
What is the CPU?
the central processing unit executes the instructions needed to run a program in a computer system
What is the ALU?
the arithmetic logic unit performs all the calculations and logical operations needed to run a program on a computer system
What is the CU?
the control unit controls the flow of data by decoding instructions to tell the memory, ALU, and other components what they are meant to do
What is the clock in a CPU?
an oscillating crystal that regulates the timing and speed of all the components’ functions within the CPU by sending out regular electrical signals
What is a register?
high speed volatile memory on the CPU that only stores a piece of info, like an instruction, before it is transferred to another component
What is a bus?
several parallel wires through which data is transmitted from one component to another
What are the key features of Von Neumann architecture?
-control unit
-shared bus
-single store of main memory for both data and instructions
How are the key features of Von Neumann architecture used?
used in combination for accessing/storing both data and instructions, which are fetched and executed sequentially through the FE cycle
What are the 3 factors that affect CPU performance?
-clock speed
-number of processor cores
-size of cache
The speed of other components (eg RAM/buses) can also affect CPU performance, although not directly
What is a processor core, and how does the number of cores affect CPU performance?
-a core is a processing unit containing an ALU, CU, cache, and registers
-more instructions can be executed per clock tick, speeding up processes on the computer system
This is known as parallel processing
Why can cache size affect the CPU’s performance in a computer system?
-the CPU always checks cache first for instructions as it is closer, before taking a longer time to check RAM
-the more cache there is, the more quick-reference instructions can be stored and used, saving time and increasing speed
What is the Fetch Execute cycle?
process where the CPU continuously retrieves instructions from main memory and executes them as required
Describe the steps involved in the Fetch Execute cycle:
fetch - the next instruction is retrieved from main memory to the CPU
decode - instruction is decoded by the CU to work out what it is
execute - instruction carried out by ALU (may also include reading/writing from/to main memory)
What is RAM? Describe its purpose:
-random access memory
-a form of volatile memory (contents lost if depowered)
-used to load programs/data before they are ran, so the CPU can access it faster than if it were stored on secondary storage
By the Stored Program Concept, the program must be in RAM before it can be executed by the CPU, so RAM is quite important.
How is main memory used on a computer system?
-every memory location has a unique address which can be accessed when required
-loads programs before they are ran, and stores the instructions/data while it is being executed
What is ROM? Describe its purpose:
-read-only memory (can’t be overwritten easily)
-non volatile
-used to store programs that start up the computer and store info about the hardware
Firmware is stored here (permament software)
What is cache?
high speed memory that stores frequently used data/instructions
What is the difference between main memory and secondary storage?
-main memory is any form of volatile storage mechanism that is directly accessible by the CPU
-secondary storage is any non-volatile storage mechanism not directly accessible by the CPU
Name 3 types of secondary storage:
-solid state (uses electrical circuits to store)
-optical disks
-magnetic
Explain how magnetic storage works:
-HDDs have layers of several spinning platters with a magnetic oxide coating
-small regions of concentric tracks are made different polarities to be read as a 1 or 0
-read 1 block at a time
Describe how optical storage works:
-laser shined on a single spiral track of stamped-in lands/pits on a spinning disk
-lands are reflective surfaces and the laser reflects off it, and is read as a 1 by a photoelectric cell
-pits are non-reflective and read as a 0
Can have CDs (700MB), DVDs (4.7GB), and Blu-Ray (25GB)
How is solid state better than magnetic storage?
-portable
-robust and quieter and faster at reading/writing data (no moving parts)
-generates less heat
-less power needed to run it
Draw the full table for comparing magnetic, solid state, and optical storage:
-cost
-capacity
-durability
-reliability
-portability
-speed of reading/writing
What is cloud storage?
an off-site secondary storage device that uses either magnetic and/or solid state
Give some pros of cloud storage:
-data is secure from on-site disasters
-data is accessible anywhere with internet (easy to share)
-could be cheaper if subscription based
-highly flexible and will grow with your data
Describe some cons of using cloud storage:
-trust placed in company (could be subject to cyber attack) and inability to retain complete control of your data
-need internet
-download/upload speeds are affected by internet connection
The data uploaded to the cloud may be accessed by third parties so you have lost complete control
Why might the use of cloud storage have increased recently?
-more mobile devices
-higher bandwidth networks (5G)
How is an embedded system different from a non-embedded system?
-embedded systems are built into a physical product with a dedicated purpose that have more ROM than RAM (eg washing machine)
-non-embedded systems are multipurpose, and have more RAM than ROM (eg smartphones)
What is the purpose of a truth table?
used to display all possible inputs and their associated outputs from a logic system
State 2 reasons why computers have more RAM than cache memory:
-RAM is cheaper per MB
-the capacity of cache is not enough to store both data and programs (only enough for frequently used instructions)
Why do computers usually have both magnetic and solid state storage?
-SSDs are more expensive per GB than magnetic
-SSDs are faster at reading/writing than HDDs, so it can store things like the OS
-magnetic can be used for mass storage, since it usually has a higher capacity
